A photonic integrated circuit is a device that uses light rather than electrons to perform a wide variety of optical functions. These optical functions are for information signals imposed on optical wavelengths, typically in the visible spectrum or near infrared 850 nm-1650 nm. Recent developments in nanostructures, metamaterials, and silicon technologies have expanded the range of possible functionalities for these highly integrated optical chips.
Externally modulated laser (EML) is one important application of the photonic integrated circuit, which combines at least one distributed laser element with an electro-absorption modulator on a single chip. Typically, the existing EMLs are designed such that the laser element and the modulator share an electrical bottom electrode (may be a highly-doped conductive substrate). This allows simple grounding of both the laser element and the modulator using the bottom electrode. Top metal electrodes of the EML may be used for biasing the laser element and the modulator and for driving the modulator with a high speed electrical signal.
However, with this typical structure, the modulator must be driven by a single-ended signal, which leads to increased power consumption of the driver and requires using expensive high breakdown technologies. One approach to resolve the problem is to separate the laser element and the modulator to different chips, which, unfortunately, increases optical loss between the laser element and the modulator and impacts output power.
Accordingly, there remains a need for EML designs to isolate top and bottom electrodes of the laser element and the modulator, while keeping the laser element and the modulator within a same chip.